The chief objective of the proposed research is to learn more about the organization and function of chromosomes in higher organisms. In particular, the biochemical organization and replication of satellite DNAs and the genes for ribosomal RNA (rDNA) will be studied in several animal systems. Certain aspects of RNA transcription in giant chromosomes will also be investigated. The nucleotide sequences of the satellite DNAs of Drosophila melanogaster will be determined by sequencing RNA transcripts from purified satellite DNA strands. The replication of satellite DNA will be examined in Drosophila embryos by means of electron microscopy. Additional information on the rolling circle model of rDNA replication will be sought in the developing oocytes of several animal species, including the toad, Xenopus. Finally, work will continue on the use of in situ nucleic acid hybridization to identify the kinds of RNA synthesized by the giant lampbrush chromosomes of Amphibia and the polytene chromosomes of Drosophila.